New Exoplanets on Google

Thoughts from Steven: Seven New Exoplanets

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The other day, I got on Google’s page and saw a doogle. In this animation, Earth looks through a telescope and sees a planet in the distance. Then, another planet pops into view. Then another. And another, until there are seven planets smiling and waving back. Earth rejoices having found seven new friends.

Without clicking on the link to see what the story was about, it was obvious that astronomers had discovered some new planets. It also appeared that these new planets were special. How? Well, when exoplanets (that is, planets outside of the solar system) were first discovered, many scientists were excited about the possibility of finding life elsewhere in the universe. At first, the only exoplanets that were known were gas giants. This type of planet that would not be able to sustain life, so initially, it was a dead end. Then, smaller exoplanets were discovered that had a density more similar to Earth, Mars, Venus, and Mercury, the rocky planets. These were “more” habitable for life, in the sense that organisms could actually live on a rocky surface. Again, the excitement was that”life could be out there!”

Curious, I followed the link. Indeed, the excitement about these seven planets was because they were even “more” likely to have life. The headline that announced these planets was, “NASA telescope reveals largest batch of Earth-size, habitable-zone planets around single star.”i Wow! Earth-sized! Habitable-zone! All we need to do is send a rocket there and greet the alien life forms waiting to meet us. Okay, that last part is a bit of an exaggeration, but NASA’s press release did include an imaginative poster encouraging people to visit TRAPPIST-1e, the name of one of these new planets.

The excitement about these planets is partly because they are also the next best place to look for life, and so close to Earth, too (40 light years away, or 235,000,000,000,000 miles away). After all, aside from the fact that the density of the planets suggesting that they are rocky, there is also evidence that at least two of planets lack a hydrogen-dominated atmosphere. As one scientist said, “The lack of smothering hydrogen-helium envelope increases the chances for habitability on these planets.”ii Reading the press release and other popular articles about these seven planets, one would be forgiven for thinking that the discovery of extraterrestrial life was just around the corner.

I wanted to read up some more on these planets. Unfortunately, the article in Nature, where the technical paper was published, could only be accessed by paying for it, so I limited myself to its abstract.iii However, even that had some interesting details. For one thing, it confirmed that these planets were not observed directly. Instead, they could only be detected when they passed in front of their star, TRAPPIST-1. This is typical. As far as I know, no exoplanet has been observed directly. Instead, they have been detected because of a wobble they cause to their star or because they cause the light from their star to dim slightly when they pass in front of it. The size and density of the planet could be inferred from this wobble and the dimming of the light. I do not have a problem with this inference: it is based on good observations and math. However, it is important that it is not observed directly, because if the existence of the planets is inferred, then how habitable they are is an inference upon an inference.

The abstract in Nature did reveal that there was a new method used to investigate these planets. By measuring the light coming from the star when a planet passed in front of them was used to make a guess about the atmosphere of these planets.iv This is likely the reason they were able to conclude that the atmosphere was not rich in hydrogen. Apparently, little else is known about the atmosphere of these planets at this time.v Without specific details of the atmosphere, it is not possible to say how habitable these planets are. Knowing that the atmosphere is not composed largely of hydrogen eliminates one possibility. Considering that there are multiple other possible atmospheres that can be just as inhospitable, eliminating one possibility does not make it more likely that the planet is habitable.

Another key reason that these planets are considered to be habitable is because these planets exist in a “habitable zone” around their star.vi This “habitable zone” is defined by how warm the planet is. Too cold, water will be frozen. Too hot, water will be a vapor. The “habitable zone” is where it is “just right” for water to be a liquid.

You may notice something. In the solar system, one planet is in the “habitable zone,” and that is Earth. For seven planets to be in the habitable zone, they must be very close to each other. Indeed, the press release says that the planets are so close to each other that to an observer on one planet, an adjacent planet would appear like our Moon. Moreover, all seven planets are closer to their star than Mercury is to the Sun.vii The reason the planets can be so close to their star and be in the “habitable zone” is because their star is a dwarf star, closer in size to Jupiterviii and therefore much cooler than our Sun.

Despite how warm the planets are, I did not read any evidence that any of these planets have water, That makes it rather moot that they are the right temperature to have liquid water. If there is no water at all it would be as inhospitable as a planet outside of the “habitable zone.” Moreover, the possibility exists that one side of each planet faces their star permanently.ix This would be like our Moon where the time of an orbit and the time of a revolution are equal so that one face of the Moon always faces the earth. Finally, these planets have a very short orbital time. The innermost of the seven planets have orbital times of 1.51, 2.42, 4.04, 6.06, 9.1, and 12.35 days!x The planet with the longest orbit completes a full “year” in twelve and a third days! Clearly, these planets deviate from Earth in numerous ways.

You may have noticed that I have been putting quotation marks around “habitable zone.” The reason I have been doing that is because the “habitable zone” is defined by precisely one factor that can affect life: the temperature. Numerous other factors that affects life (radiation from the star, presence of water, tidal affects from adjacent bodies, axial tilt, weather, complex organic chemistry, genetic information, just to name a few) are not factored into the “habitable zone.” Why then is it called the “habitable zone?” I think it is because scientists know that water is crucial for life. However, with an evolutionary worldview, these scientists think that water is a prerequisite for life, that is, the presence of water allows the creation of life to begin. The idea that the presence of water portends the occurrence of life is the largest inference that these scientists make. To them, it is inevitable that a planet in the “habitable zone” will be found with life.

Remember when I said that the very existence of these planets is an inference? That is not a bad inference. It makes sense in light of the evidence. What of the inference that these seven planets exist in a “habitable zone” and that there is a possibility that life could exist on one of these planets? That is an inference based on a worldview rather than strictly on the evidence. The numerous differences between these planets and Earth (orbiting a dwarf star, closely adjacent orbits, short orbits, one side facing the star) show that these factors, which can all affect life, are less important than the worldview of the astronomers at NASA. I believe that this is further evidence that the hunt for extraterrestrial life is driven by the evolutionary worldview rather than by any good indication that life exists elsewhere in the universe.

iNASA (2017) “NASA telescope reveals largest batch of Earth-size, habitable-zone planets around single star” retrieved from https://www.nasa.gov/press-release/nasa-telescope-reveals-largest-batch-of-earth-size-habitable-zone-planets-around on February 22, 2017

iiNASA (2017) “NASA’s Hubble Telescope Makes First Atmospheric Study of Earth-Sized Exoplanets” retrieved from https://www.nasa.gov/press-release/nasa-telescope-reveals-largest-batch-of-earth-size-habitable-zone-planets-around on February 22, 2017

iiiMichael Gillon, Amaury Triaud, Brive-Olivier Demory, Emmanuel Jehlm, Eric Agol, Kantherine Deck, Susan Lederer, Jullen de Wit, Artem Burdanov, James Ingalls, Emeline Bolmont, Jeremy Leconte, Sean Raymond, Frank Selala, Martin Turbet, Khalid Barkaout, Adam Burgasser, Matthew Burleigh, Sean Carey, Aleksander Chaushev, Chris Copperwheat, Laetitla Delrez, Catarina Fernandes, Daniel Holdsworth, Enrico Kotze (2017) “Seven temperate terrestrial planets around the nearby ultracool dwarf star TRAPPIST-1” Nature, retrieved from http://www.nature.com/nature/journal/v542/n7642/full/nature21360.html

ivIbid.

vNASA (2017) “NASA’s Hubble Telescope Makes First Atmospheric Study of Earth-Sized Exoplanets” retrieved from https://www.nasa.gov/press-release/nasa-telescope-reveals-largest-batch-of-earth-size-habitable-zone-planets-around on February 22, 2017

viNASA (2017) “NASA telescope reveals largest batch of Earth-size, habitable-zone planets around single star” retrieved from https://www.nasa.gov/press-release/nasa-telescope-reveals-largest-batch-of-earth-size-habitable-zone-planets-around on February 22, 2017

viiIbid.

viiiMichael Gillon, Amaury Triaud, Brive-Olivier Demory, Emmanuel Jehlm, Eric Agol, Kantherine Deck, Susan Lederer, Jullen de Wit, Artem Burdanov, James Ingalls, Emeline Bolmont, Jeremy Leconte, Sean Raymond, Frank Selala, Martin Turbet, Khalid Barkaout, Adam Burgasser, Matthew Burleigh, Sean Carey, Aleksander Chaushev, Chris Copperwheat, Laetitla Delrez, Catarina Fernandes, Daniel Holdsworth, Enrico Kotze (2017) “Seven temperate terrestrial planets around the nearby ultracool dwarf star TRAPPIST-1” Nature, retrieved from http://www.nature.com/nature/journal/v542/n7642/full/nature21360.html

ixNASA (2017) “NASA telescope reveals largest batch of Earth-size, habitable-zone planets around single star” retrieved from https://www.nasa.gov/press-release/nasa-telescope-reveals-largest-batch-of-earth-size-habitable-zone-planets-around on February 22, 2017

xMichael Gillon, Amaury Triaud, Brive-Olivier Demory, Emmanuel Jehlm, Eric Agol, Kantherine Deck, Susan Lederer, Jullen de Wit, Artem Burdanov, James Ingalls, Emeline Bolmont, Jeremy Leconte, Sean Raymond, Frank Selala, Martin Turbet, Khalid Barkaout, Adam Burgasser, Matthew Burleigh, Sean Carey, Aleksander Chaushev, Chris Copperwheat, Laetitla Delrez, Catarina Fernandes, Daniel Holdsworth, Enrico Kotze (2017) “Seven temperate terrestrial planets around the nearby ultracool dwarf star TRAPPIST-1” Nature, retrieved from http://www.nature.com/nature/journal/v542/n7642/full/nature21360.html

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